Water Rocket Forum

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A water rocket is a type of model rocket using water as its reaction mass. The pressure vessel (the engine of the rocket) is constructed from thin plastic or other non metallic materials (usually a used plastic soft drink bottle) weighing 1,500 grams or less. The water is forced out by compressed air. It is an example of Newton's third law of motion.

I would like to try to set a new record for Class D rockets (unreinforced bottle), but I have a few questions abuot competition rules:

1. Can I use my self-made LaunchPad Altimeter (developed by U.S. Water Rockets) or I have to buy a commercial altimeter with display?

2. Can I set the parachute deploy delay about 1,5 or 2 seconds past apogee to deploy the parachute when rocket is about 30 meters high? The rocket descent speed will be less than 10 meter per second when Landing, but, just after apogee, its descent ratio will be more than 10 meters/second. Is this OK, according to rules?

4. If I use the PVC tube as a shield (see question n. 3), is it OK to stay at about 2 feet from the pressurized rocket (remember the tube is 4 mm thick and very strong, plus I have ear protection and glasses)?

5. Must I keep the rocket pressurized for 10 minutes before launch if I use a hand pump for bikes?

Thank you very much for paying attention! You are awesome, guys!

P.S.: I'm sure I made lot of language mistakes above. Please forgive me, I'm only 15 and I write from Italy.

T.Valerio & Soci - Santo Stefano Water Rockets Team

Take a look at our:Facebook page facebook.com/razzi.s.stefano/YouTube channel youtube.com/channel/UCn85UPNv8vw84-irTR4Db7gg

Sorry about the delay but our hosting company decided to change the server our database was on (without telling us) and it took a day to get the forum back online.

To answer your questions,

1. The altimeter by US Water Rockets is a good question. When the rules were developed, this did not exist. Since that altimeter is built using "off the shelf" commercial products (the pressure sensor board and the TI Launchpad, we can assume some measure of accuracy as far as the hardware goes and each one will be using the same software makes it similar to a commercial altimeter and that it should be allowed. The original intent of the rule was to prevent each team from making a homemade altimeter using varied designs and accuracy levels. Does any other team object to allowing it to be used?

2. You can delay the deploy past apogee as long as the rocket is traveling at less than the max allowed decent speed at touchdown.

3. and 4. For simplicity sake, the long hose to meet minimum safe distance makes more sense and will be more economical to building a protective housing to contain the rocket prior to launch (this makes it easier to observe the rocket prior to launch). PVC will shatter if subjected to a shock such as an exploding rocket as well.

5. No if you compress your own air and fill the rocket by pumping it (either manually or with a compressor) you will already meet the requirement with the time it takes you to pump the rocket to pressure. This rule was designed to prevent what is called a "stomp rocket" where the rocket is pressurized and launched rapidly. The advantage to doing that would be that you would be able to construct a lighter and less sturdy rocket and teams using that method would have an unfair advantage over a team filling their rocket slowly.

Lisa Walker,Forum Administrator. The Water Rocket Achievement World Record Association

Per the Class D rules: "Pressure vessel and fuselage of rocket must be constructed from a single unmodified soft drink bottle which cannot exceed 2 liters (labeled capacity) volume. (commercially produced stretched or modified bottles such as the U14 stretched water rocket bottle by Anti Gravity Research are not allowed).."

Are plastic (PET) liquor bottles included in this category? They are about four times as thick as the standard "soda" bottles and should hold much higher pressures.

In the spirit of fair competition I personally do not think they should be allowed, although I am currently building a booze bottle rocket for...research.

Is a launch valid if the rocket self-laucnhes (there is not countdown and nobody pulls the release string) because of Gardena quick connector failure? I think it should not be valid but I want to be sure.

To understand what happened, please watch this video

T.Valerio & Soci - Santo Stefano Water Rockets Team

Take a look at our:Facebook page facebook.com/razzi.s.stefano/YouTube channel youtube.com/channel/UCn85UPNv8vw84-irTR4Db7gg

Sorry about the delay but our hosting company decided to change the server our database was on (without telling us) and it took a day to get the forum back online.

To answer your questions,

1. The altimeter by US Water Rockets is a good question. When the rules were developed, this did not exist. Since that altimeter is built using "off the shelf" commercial products (the pressure sensor board and the TI Launchpad, we can assume some measure of accuracy as far as the hardware goes and each one will be using the same software makes it similar to a commercial altimeter and that it should be allowed. The original intent of the rule was to prevent each team from making a homemade altimeter using varied designs and accuracy levels. Does any other team object to allowing it to be used?

Although I would like the Launchpad Altimeter to be specifically allowed I believe additional verification should be required in order to maintain the friendly nature of competition here. Also, if it is to be allowed, the rules should be revised in order to avoid any ambiguity and to continue to promote fair competition.

I have built the TI Launchpad Altimeter following the instructions to the letter and had acceptable results when comparing it's reported altitude against the Estes peak altimeter so I had a measure of confidence in its accuracy. My main purpose in building it, however, was to have a reliable parachute deployment system. It did not fit in a standard FTC, though, so I built and ground tested an altimeter that uses the same altitude sensor and MSP430, but does away with the Launchpad board similar to the one posted here by Uberpixel. http://www.wra2.org/forum/viewtopic.php?f=5&t=2805 I have not compared this second altimeter against a known standard and have no idea how it will perform, in terms of accuracy.

As to the hardware being identical, in principle this is true, though there is no quality control similar to mass produced hobby altimeters. Every build an individual makes is unique. I believe this does not meet the definition of "mass produced"

As to "...each one will be using the same software," the unscrupulous could easily load their own custom software in order to gain an unfair advantage.

I like the simple rules as they are. They are fair and uniform, promoting fun and fair competition.

I wish I had weighed in on this sooner, as there is a record submission in progress at this time and I only hope the best for them, however, at this time I do not support the use of the self-built Launchpad Altimeter for use in competition.

If it is to be allowed, then more discussion and verification is required.

motorcyclepilot wrote:Per the Class D rules: "Pressure vessel and fuselage of rocket must be constructed from a single unmodified soft drink bottle which cannot exceed 2 liters (labeled capacity) volume. (commercially produced stretched or modified bottles such as the U14 stretched water rocket bottle by Anti Gravity Research are not allowed).."

Are plastic (PET) liquor bottles included in this category? They are about four times as thick as the standard "soda" bottles and should hold much higher pressures.

The class D rules permit only up to 100 psi of pressure. So if you use a thicker bottle, you're just giving yourself a weight penalty, since a thin soft drink bottle can easily withstand 100 psi.